This invention relates generally to electrical power distribution systems and particularly to apparatus and methods for balancing the loads on the individual phases of polyphase distribution systems.
In polyphase power distribution systems, it is desirable to balance the loads on the individual phases of the system. Ideally, the loads on all the phases should be equal (that is, balanced) because a polyphase system delivers maximum power when all the phases are supplying their maximum rated current. For example, it would be unacceptable for the loads on one phase to exceed its current rating while the loads on another phase were below its current rating. As used herein, the word xe2x80x9cbalancedxe2x80x9d means that the loads on the individual phases are equal within acceptable limits for the power distribution system in use; however, it does not mean that the loads on each phase are exactly equal or that the loads on all phases are non-zero.
Traditionally, load-balancing is accomplished by the electrician wiring the system. To do this the electrician must keep an accounting of the power requirements of all the loads on each phase and add loads to, or remove loads from, each phase as necessary to achieve the desired balance. This method is not only tedious and time consuming during the installation of the system but it also requires the services of a skilled electrician whenever loads are added or removed throughout the life of the system.
It is therefore an object of this invention to provide a simple means for achieving acceptable load balancing without the need for wiring, or rewiring, by a skilled electrician.
U.S. Pat. No. 5,934,096 discloses a wiring system for commercial refrigeration which permits power to be balanced among three phases of electrical power. Patent ""096, in the paragraph extending from column 7, line 50 to column 8, line 4, states that an installer can choose which phases of the electrical power will be sent to the lights and fans and which to the electric defrost by simple rotation of the connectors relative to each other. This requires that the installer know the load distribution on the three phases in order to choose which relative orientation of the connectors to use. In the present invention, such knowledge is not required.
The invention comprises an apparatus, and a simple method, for connecting loads to a polyphase power distribution system in such a way that the loads on the individual phases of the system are balanced. The balancing is accomplished without requiring the installer to know the load distribution on the, phases.
The apparatus comprises an equipment rack or frame having multiple equipment mounting positions and multiple single-phase electrical outlets, or receptacles, adjacent to the mounting positions. Each outlet is connected to one of the N phases of a polyphase power distribution system in such a way that when pieces of equipment are mounted in the rack and plugged into adjacent outlets in an orderly fashion, adequate load balancing is accomplished automatically.
For example, in a three-phase system, the outlets are wired to the phases as follows: a first outlet group to phase 1, a second outlet group to phase 2, a third outlet group to phase 3, a fourth outlet group to phase 1, a fifth outlet group to phase 2, a sixth outlet group to phase 3, an ith outlet group to phase 1, an (1+i)th outlet group to phase 2, an (2+i)th outlet group to phase 3, and so on to the total number of outlets in the apparatus. The outlets and the mounting positions for the loads are physically arranged on the rack in rows and columns such that the natural row-and-column order of mounting the loads contiguously in the rack leads to plugging the loads into the outlet groups in counting-number sequence. In other words, the first loads are plugged into the first outlet group, the second loads into outlet 2, the third loads into outlet 3, etc.
Preferably, the apparatus also provides another group of outlets, adjacent to each mounting position, which is connected to and supplied by a different source. The additional outlets permit redundant power supplies in each piece of equipment to be connected to separate and independent sources for greater reliability.
As used herein, the word xe2x80x9coutletxe2x80x9d means the point at which a load can be connected to a power distribution system while the word xe2x80x9creceptaclexe2x80x9d refers to the hardware device for receiving an electrical plug. The term xe2x80x9coutletxe2x80x9d is not limited to specific type of hardware.